1. Field of the Invention
The present invention relates to constructing and broadcasting a multi-screen broadcasting program using a transport stream in digital broadcasting, and more particularly to an apparatus and method for decoding the constructed transport stream to restore image and voice signals.
2. Description of the Related Art
Recently, digital broadcasting services have been provided through a broadcasting system based on ISO (International Organization for Standard)/IEC (International Electrotechnical Commission) 13818-1 and ISO/IEC 13818-2, which are international standards.
The ISO/IEC 13818-2 refers to MPEG-2 video data and is an international standard for compressing a moving image. The ISO/IEC 13818-1 is an international standard for multiplexing compressed image data, voice data, and additional data in a broadcasting transmission side. It also relates to demultiplexing this data in the broadcasting reception side, so as to transmit this data at one time. The additional data includes synchronization information for synchronizing the image data and voice data in the broadcasting reception side, e.g., information about a program, etc.
There are two types of MPEG-2 systems. One type is called a “program stream”, which includes a single program as MPEG-1 system. The other type is called a “transport stream”, which is designed to transmit bit streams and may include a plurality of programs.
FIG. 1 is a block diagram illustrating the construction of a conventional broadcasting service system to provide a plurality of broadcasting content.
According to such conventional broadcasting service systems, as shown in FIG. 1, a broadcaster receives various digital broadcasting content, such as a news 101, a drama 102, and a football game 103, from a broadcasting content provider. Then, the broadcaster multiplexes the received digital broadcasting content through a multiplexer 11, and broadcasts the multiplexed content as a multi-program transport stream (MPTS) 100. In this case, the broadcasting of the contents is realized through a terrestrial wave, a satellite, a cable, etc.
A broadcasting splitter 12 in a subscriber side splits the broadcasted MPTS 100 into a plurality of single-program transport streams (SPTSs) 104-1 and 104-2 for each digital content. It then provides digital content 101 and 102 to subscribers according to the selection of each subscriber.
The MPTS 100, which is a broadcasting stream including a plurality of digital broadcasting content 101, 102, and 103, includes program ID (PID) information for each of the digital broadcasting content 101, 102, and 103 and the like. This enables, the digital broadcasting content 101, 102, and 103 to be split from each other through the broadcasting splitter 12 in the subscriber side.
Each digital broadcasting content is an SPTS, in which compressed image data, voice data, and additional data are included.
FIG. 2 illustrates the structure of an SPTS that includes image, voice, and data packets.
A transport stream for one broadcast is divided into image data 22 containing image information, audio data 24 containing audio information, and additional data 26 containing information relating to broadcasting and additional services. In addition, each data has a header 21, 23, or 25, in which information necessary for demultiplexing and decoding is recorded.
A transport stream header is added to the data structure shown in FIG. 2, thereby constructing and transmitting a transport stream. Herein, the procedure of constructing a transport stream has no direct relation with the present invention, so detailed description thereof will be omitted.
FIG. 3 is a block diagram of a conventional transport stream receiving apparatus in a digital broadcasting system.
A conventional transport stream receiving apparatus in a digital broadcasting system includes a channel classifying decoder 31, a transport stream demultiplexer 32, a video decoder 33, an audio decoder 35, and a data processing unit 34. The channel classifying decoder 31 receives a multi-program transport stream (MPTS) and the channel selection information input by the user and transmits only a single-program transport stream (SPTS) of a selected channel to the transport stream demultiplexer 32. The transport stream demultiplexer 32 demultiplexes the received SPTS, and separately outputs an image packet, a voice packet, and a data packet, which have been included in the SPTS. The video decoder 33 decodes the image packet. The audio decoder 35 decodes the voice packet. The data processing unit 34 decodes the data packet and provides the video decoder 33 and audio decoder 35 with a clock pulse for synchronizing voice and image data.
The clock pulse from the data processing unit 34 provides the time periods required for the decoding operation of the video decoder 33 and audio decoder 35. Accordingly, it is used to synchronize the voice and the image data.
TABLE 1
Table 1 illustrates a program access table (PAT) and a program mapping table (PMT). It is used by a program demultiplexed by the transport stream demultiplexer 32 in the conventional transport stream receiving apparatus for the digital broadcasting system.
Referring to Table 1, the PAT informs that there is one program (program_number) in a transport stream transmitted through a selected channel. The program ID (PMT_PID) of a channel selected by the user is “0x0A0”. The transport stream demultiplexer 32 analyzes the PMT_PID (e.g. “0x0A0”) corresponding to an appointed program_number obtained by analyzing the PAT.
The transport stream demultiplexer 32 analyzes the PMT having the program ID (PMT_PID) of “0x0A0.” The transport stream demultiplexer 32 obtains PID information of a basic stream, video information (SDTV class or HDTV class) (e.g. “0x0A1”) and audio information (MPEG audio or AC-3 audio) (e.g. “0x0A5” representing MPEG audio in Table 1). These are actual components of a program and information about data (e.g. “0x00AA”) if it is necessary. The transport stream demultiplexer 32 transmits video, audio, and data information according to information included in Table 1 to corresponding decoders (e.g. decoders 33, 34, and 35). The transmitted information is decoded at a predetermined time and is output to an exterior device. This allows a user to view the relevant program.
As described above, a transport stream based on Table 1 is configured with a program which includes one piece of video information, one piece of audio information, and data information.
Meanwhile, a transport stream may include a multi-screen, which will now be described with reference to Table 2.
TABLE 2
Table 2 illustrates a program access table (PAT) and a program mapping table (PMT). It is used by a program demultiplexed by the transport stream demultiplexer 32 of the conventional transport stream receiving apparatus. It can provide a multi-screen picture in a digital broadcasting system.
Referring to Table 2, the PAT informs that there is one program (program_number) in a transport stream transmitted through a selected channel. The program ID (PMT_PID) of the channel selected by the user is “0x0A0”. The transport stream demultiplexer 32 analyzes the PMT_PID (e.g. “0x0A0”) corresponding to an appointed program_number obtained by analyzing the PAT.
The transport stream demultiplexer 32 analyzes the PMT having the program ID (PMT_PID) of “0x0A0.” The transport stream demultiplexer 32 obtains PID information of a basic stream, a plurality of video information (SDTV class or HDTV class) (e.g. “0x0A1”, “0x0A2”, “0x0A3”, and “0x0A4”) and audio information (MPEG audio, AC-3 audio, etc.) (e.g. “0x0A5” representing MPEG audio in Table 2). These are actual components of a program and information about data (e.g. “0x0AA”) if it is necessary. The transport stream demultiplexer 32 transmits video, audio, and data information according to information included in Table 2 to corresponding decoders (e.g. decoders 33, 34, and 35). The transmitted information is decoded at a predetermined time and is output to an exterior device. This allows a user to view the relevant program.
However, in such conventional transport stream receiving apparatuses, a PMT must be analyzed in order to obtain information about a multi-screen. This is provided to improve the quality of a digital broadcasting service. Also it is impossible to control screen configuration based on priorities among a plurality of image information which form the multi-screen.